Fluid level measurement device

Abstract

The present invention relates to a device ( 10 ) for providing a gas composition compensated acoustic measurement of the level of a liquid ( 16 ) in a tank ( 18 ). The device comprises a transducer ( 14 ) arranged outside said liquid for transmitting and receiving acoustic signals, and a waveguide ( 12 ) connected to said transducer and extending into the liquid. The device further comprises means for feeding a flow of fluid from said tank into the part of said waveguide which is located above the liquid level. That results in that the gas composition become essentially similar throughout the whole of the waveguide located above the liquid level, whereby the level measurement using the speed of sound in the waveguide, which speed is dependant on gas composition, becomes very accurate.

1. A device for measuring the level of a fluid in a tank using low frequency acoustic pulses, said device comprising:
 a transducer means for transmitting and receiving acoustic pulses, and 
 a waveguide connected to said transducer and extending into the fluid, said waveguide having a reference part located above the fluid surface, wherein
 said waveguide reference part is provided with at least one bend in a plane essentially parallel to the surface of the fluid. 
 
 
     
     
       2. A device according to  claim 1 , wherein said waveguide reference part is provided with a plurality of bends in said plane. 
     
     
       3. A device according to  claim 1 , wherein said acoustic pulses have a wavelength of at least twice a diameter of the waveguide to ensure plane wave propagation. 
     
     
       4. A device according to  claim 1 , wherein said waveguide reference part is provided in a plurality of 360°-turns in said plane. 
     
     
       5. A device according to  claim 4 , wherein said waveguide reference part is helical. 
     
     
       6. A device according to  claim 4 , wherein said waveguide reference part has the form of a flat spiral. 
     
     
       7. A device according to  claim 1 , further comprising a second waveguide extending into the fluid. 
     
     
       8. A device according to  claim 7 , wherein said waveguide and said second waveguide are connected to said transducer on opposite sides of said transducer respectively. 
     
     
       9. A device according to  claim 7 , wherein said waveguide and said second waveguide have a common reference part. 
     
     
       10. A device according to  claim 7 , further comprising a second transducer, whereby said second waveguide is connected to said second transducer. 
     
     
       11. A device according to  claim 7 , further comprising an electronic control device arranged outside of the tank, whereby the transducer(s) are arranged inside the tank.